Method of making a composite abrasive wheel



Nov. 22, 1938. E B. SANFORD E 2,137,986

METHOD OE MAKING A COMPOSITE ABRAsIvE WHEEL. Y Y

' Filed Jan. l2, 1937 EN n* FEg. 1.

` Baalis Sanford l @Mom/WM Patented Nov. 22, 1938 UNITED STATE PATMETHOD OFMAKING A COMPOSITE ABRASIVE WHEEL num suma, worcester, Mass.,mmm io'Norton Company, Worcester, Mass., a corporation of MassachusettsApplication January-12, 1931, sex-m No. 120.276

3 Claims.

This invention relates to the manufacture of composite grinding wheelsand particularly wheels of the type which have a solid supporting centercarrying a rim of bonded diamonds or other l abrasive material.

It has been proposed to make a grinding wheel by first premolding asupporting center of a suitable material, suchgas a resinoid bodypressed to its final form, and then. compressing a rim of l abrasivematerial onto the periphery of the support. Various problems areinvolved in the manufacture of that type of wheel and particularly incontrolling the structure and density of the abra- 'sive rim and ofinsuring a substantially integral union between the rim and the support.In that method, the central resinoid supporting body formed a part ofthe mold and it was necessary to compress the abrasive mixture withinthe mold space lying between the central support and the mold band to athickness which was materially less than that of the central support.This required cutting away the face of the central support in order thatit would not project beyond the abrasive rim. The objects of the presentinvention are to provide a method of making such a composite wheel whichwill serve for shaping an vabrasive rim and uniting it integrally with acentral support prior to the step of maturing the bond, and to provide amold device which will insure making duplicate structures withoutrequiring that either the abrasive material or the support be cut awayto shape the article further after the molding operation. Furtherobjects will be apparent in the following disclosure.

One embodiment of a mold structure suitable for carrying out the methodof this invention is illustrated in the drawing in which:

Fig. l is a diametrical section through the mold 4D showing the centralwheel support and the abra'- sive mixture in the mold cavity prior tothe pressing operation;

Fig. 2 is a similar view showing the mold closed and the parts in theirnal pressed condition;

and

Fig. 3 shows the mold parts in' a disassembled relation, which indicateshow the grinding wheel is removed therefrom. s

In accordance with this invention, I have provided a special moldconstruction by which an abrasive and bond mixture may be compacted ontoa supporting center. This may comprise a mold band I0 of substantiallyL-shaped cross section which has two internal annular surfaces ofdiierent diameters. 'I'he larger annular surfaceV II is arranged tocarry a ring I2 slidably fitted therein. The outer plane surface of thering I2 is ush with the bottom of the mold band when its upper surfacecontacts with the shoulder .i3 of the ring I0. Slidably mounted within'5' the ring I2 is a central disk shaped mold plate Il which is adaptedto support the wheel center I5 made of a resinoid or rubber which hasbeen previouslygmolded by another operation. In the -present embodiment,the premolded wheel center I5 and the mold plate I4 are disk shapedbodies having the same diameter. Mounted above the center support I5 intheir assembled relationship is a further mold plate I6 which isslidable against the inner surface Il of the upper 15 smaller diameteredportion of the mold band I0. .This arrangement is such that when theparts are assembled as shown in Fig. 1, the'mold band III, the twoplates I4 and I6, themold ring I2 and the wheel center I5 leave anannular mold "20 cavity I8 which is considerably thicker than the plateI5, as indicated in Fig. 1, whereby this cavity I8 may be filled with amixture of abrasive grains and a suitable bond therefor whichmay bethereafter compacted onto and integrally united with the supporting bodyI5. The band I0 and ring I2 could be made integral as an L- shaped mold(in cross section) but it is preferable to have them separable for thepurpose of removing the molded body. 30

'I'he central wheel support I5 is made in a separate operation of asuitable material, which .is preferably of the same type as 'that usedfor the vabrasive bond. That i's, a resinoid support may be used for aresinoid'and abrasive rim and a rubber support for a rimof rubber andabrasive, but other materials may be usedfor the central support, ifdesired. The resinoid may beV a V "Bakelite phenolic aldehydecondensation product or other synthetic material capable of being y heatset to a hard non-plastic condition, and various fillers, such as woodiiour, silica, etc., may be incorporated therein in suitable amounts toinsure that its volume will not change materiallyA during the iinalpressing operation involved in mounting the abrasive rim thereon. Thesupport I5 may be pressed in a suitable mold to the disk shape shown inthe drawing, or other requiredl shape, and it may be left in itsunconverted state, if desired, untilafter the rim has been` pressedthereon. In that case, the uncured body I5 is in a plastic condition andit may be made slightly over size in thickness, as predetermined to givea required plastic ow, outwardly into a firm union with the abrasive rimduring the iinal 5 5' during the nal molding step.

Likewise, the support I5 may be made of vulcanized hard rubb'er compoundor of a yvulcanizable compound of raw rubber, sulfur and an acceleratorproportioned to form hard rubber. In

either case, the rubber compound should beinitially pressed tosubstantially its final volume before it is assembled with the rimmaterial. 'Ihe rubber compound may include various well known fillersand which may be proportioned to insure a uniform volume for ythe rubberbody.

Y If the mold parts I Il, I2 and I4 are assembled as indicated in Fig.1, with the part I4 temporarily mounted on shims to hold it in theindicated position, then the previously molded sup-` port IB may be laidon this plate Ilin a central position as indicated. If the wheel is tohave a central hole, a pin 20 of suitable shape may be inserted in holesthrough the plates I4 and I6 in order to prevent distortion of thesupport I5. The helghth of the shim which positions the plate Il willhave been previously determined to provide a space I8 in the mold whichis suillcient for holding the correct amount of abrasive and bondmixture to be compacted in place. This initial cavity may be twice aslarge as the .nal

, pressed rim material. A

This abrasive and bond mixture may be made of suitable abrasivematerial, such as diamond grains of desired grit size, e. g. 100 grit,rincorporated with a heat settable, organic bond having the capacity ofbeing plastic and owing when compressed in the mold so as to make anintegral union with the body I5. Of the various organic materials'whichmay be employed for this purppose I may utilize an unconverted resinoidpowder of the type of Bakelite phenolic formaldehyde condensationproduct together with inert fillers, if desired, such as asbestos, woodpowder, silica or other pulverized mineral substances. A precalculatedamount of the mixture of abrasive grainsand the bond, such as 25 to 50%by volume of diamonds and 75 to 50% of resinoid bond, is then placed inthe mold cavity I8, as shown in Fig. 1, and carefully leveled olf andsuch other precautions as may be needed are taken to insure a uniformdistribution of the material within the annular space. Then the moldplate I6 is slidably fitted within the mold band I and the assembly isplaced in a power press with the shims originally placed under the moldplate I 4 now removed.

' Upon applying pressure to the top of the mold plate I6 and the bottomsof the band I0 and ring l2, the material in the cavity I8 will becompacted .while lateral pressure is applied to the side of the resinoidsupport I5. This pressure will close the mold or bring all of its outerfaces into alignment with two parallel planes as indicated in Fig. 2;and the material I8 will have been compacted to the exact thickness ofthe premolded central support I5, since the mold parts will have beensized for this result. If the premolded support I has not been convertedby heat to the solid, non-plastic condition then the pressure of theplates I4 and I6 thereon will arenoso v lpositions, the outer faces ofthe plates and ring will be in the planes of the two Vfaces of the moldband and the annular abrasive material I8 will have been compacted tothe same thickness Aas that of the center support I5. Hence, it is notnecessary to shave ofi' or to grind away either the surface ofthesupport I5 or the side of the abrasive rim I8 to insure that thesides of the two parts of the grinding wheel are in two par- 'allelplanes.

I'he mold with its compacted mass, as shown in Fig. 2, may be subjectedto heat and the article thus cured while under pressure. In this case, aset screw 22 is threaded through the mold band I0 so as to engage agroove 2l in the mold ring I2 and lock the parts in assembledrelationship. This screw is to be removed later for disassembling themold parts. It is equally feasible to remove the molded article from themold and to cure it in a separate apparatus as desired, so as -toconvert the resinoid or rubber material to its solid iniusiblecondition. Standard practice may be followed for the curing operation.

The mold'assembly has been so constructed thatthe molded article may bereadily removed therefrom either before or after the heating or curingoperation. As indicated in Fig. 3, it is merely sufficient to loosen theset screw 22 and force the mold plate I6 downwardly through the moldband Ill and thus drive the plate I4 and ring I2 out of the bandand-leave the molded grinding wheel exposed. When the band I0 and theupper plate I6 have been removed, the molded article may be taken fromits lower support and treated as desired.

It will now be appreciated that I have thus provided a special type ofmold and a method whereby a precalculated amount of abrasive and bondmay be pressure molded onto the periphery of a central support ofsuitable material. The molding of the abrasive rim is done independentlyof anyv pressure applied. to the support, hence it may be compacted toany desired density, depending on the proportions and weights ofabrasive and bond selected. 'I'his method insures a strong union withthe periphery of the support, and particularly where the latter is notheat set prior to` the pressing operation and is caused to flow radiallyoutwardly by pressure applied to the plates I4 and I6 while the bond andabrasive mixture is being pressed by the ring I 2 and associated parts.

I claim: t

1. The method ,of making a composite abrasive wheel comprising the stepsof premolding a heat settable compound to form a central support havingsubstantially its nal volume, providing a mixture of abrasive grains anda heat settable plastic bond proportioned in amount to form an abrasiverim of required width and the same lthickness as the central supportwhen compacted to its nal density, confining the support within a moldwhich provides walls defining a mold cavity around the support which ishigher than thel thickness of the support and will hold theprecalculated amount of abrasive and bond, and

then compressing the abrasive and bond laterally until it attains the'same thickness as the support and is united therewith, but withoutapplying pressure directly to the support, after which the its nal,hard, non-plastic condition prior to the step of molding the abrasiverim thereon.

3. 'I'he method of making a composite Wheel according to claim 1,wherein the central support is made slightly oversize in thickness andthe rim is initially compressed to the thickness of the= support, afterwhich the rim and support are compressed simultaneously to cause lateralow thereof into a firm union.

BAALIS SANFORD.

